1. Field of the Invention
The present invention relates generally to electronic circuits and, in particular, to an enable circuit that integrates thermal shutdown capability.
2. Discussion of the Prior Art
Enable circuits for providing biasing current to an associated integrated circuit (IC) are well known. Typically, in addition to meeting their primary function of providing drive to the associated IC in response to assertion of an on/off input signal, enable circuits are also designed to minimize standby current when the input signal is off.
Conventional integrated circuits minimize current draw from the supply by disconnecting the supply when the integrated circuit is off. However, there may be applications which require that the supply remain connected even though the particular integrated circuit is not in use. For example, in automobiles it is desirable to connect numerous circuits directly to the battery so that each of these circuits may be used when the ignition switch is turned off. These circuits must be designed to draw low standby current to prevent battery discharge when the car is not driven for extended periods of time.
In addition to providing for minimized standby current, it is also desirable to provide thermal shutdown capability for the integrated circuit if its temperature exceeds a predefined threshold. Thermal shutdown is necessary because of performance drifts in the circuit when the temperature threshold is exceeded.
To achieve thermal shutdown of a particular integrated circuit typically requires utilization of a dedicated thermal shutdown circuit separate from the integrated circuit to be protected. The separate thermal shutdown circuit monitors temperature and shuts the integrated circuit off when its temperature exceeds the predefined threshold. While usually located on the same chip as the integrated circuit to be protected, the thermal shutdown circuit is often as complex as the enable circuit itself. Typically, the thermal shutdown circuit is connected to the output of the enable circuit to override that output when the threshold temperature is exceeded. These separate thermal shutdown circuits require additional die area, thereby decreasing yield and increasing product cost.